Enzymatic fuel cell

ABSTRACT

Provided is a battery comprising a first compartment, a second compartment and a barrier separating the first and second compartments, wherein the barrier comprises a proton transporting moiety.

[0001] The present invention relates to batteries, including fuel cellsand re-chargeable fuel cells, for use in powering electrical devices.

[0002] Batteries such as fuel cells are useful for the direct conversionof chemical energy into electrical energy. Fuel cells are typically madeup of three chambers separated by two porous electrodes. A fuel chamberserves to introduce a fuel, typically hydrogen gas, which can begenerated in situ by “reforming” hydrocarbons such as methane withsteam, so that the hydrogen contacts H₂O at the first electrode, where,when a circuit is formed between the electrodes, a reaction producingelectrons and hydronium (H₃O⁺) ions is catalyzed.

2H₂O+H₂Z,900 2H₃O⁺+2{overscore (e)}  (1)

[0003] A central chamber can comprise an electrolyte. The centralchamber acts to convey hydronium ions from the first electrode to thesecond electrode. The second electrode provides an interface with arecipient molecule, typically oxygen, found in the third chamber. Therecipient molecule receives the electrons conveyed by the circuit.

2HO⁺+½O₂+2{overscore (e)}z,900 3H₂O   (2)

[0004] The electrolyte element of the fuel cell can be, for example, aconductive polymer material such as a hydrated polymer containingsulfonic acid groups on perfluoroethylene side chains on aperfluoroethylene backbone such as Nafion™ (du Pont de Nemours,Wilmington, DE) or like polymers available from Dow Chemical Co.,Midland, Mich. Other electrolytes include alkaline solutions (such as 35wt %, 50 wt % or 85 wt % KOH), acid solutions (such as concentratedphosphoric acid), molten electrolytes (such as molten metal carbonate),and solid electrolytes (such as solid oxides such as yttria(Y₂O₃)-stabilized zirconia (ZrO₂)). Liquid electrolytes are oftenretained in a porous matrix. Such fuel cells are described, for example,in “Fuel Cells,” Kirk-Othmer Encyclopedia of Chemical Technology, FourthEdition, Vol. 11, pp. 1098-1121.

[0005] These types of fuel cells typically operate at temperatures fromabout 80° C. to about 1,000° C. The shortcomings of the technologyinclude short operational lifetimes due to catalyst poisoning fromcontaminants, high initial costs, and the practical restrictions ondevices that operate at relatively high to extremely high temperatures.

[0006] The present invention provides a fuel cell technology thatemploys molecules used in biological processes to create fuel cells thatoperate at moderate temperatures and without the presence of harshchemicals maintained at high temperatures, which can lead to corrosionof the cell components. While the fuel used in the fuel cells of theinvention are more complex, they are readily available and suitablypriced for a number of applications, such as power supplies for mobilecomputing or telephone devices. It is anticipated that fuel cells of theinvention can be configured such that a 300 cc cell has a capacity of asmuch as 80 W•h—and thus can have more capacity than a comparably sizedbattery for a laptop computer—and that such cells could have stillgreater capacity. Thus, it is believed that the fuel cells of theinvention can be used to increase capacity, and/or decrease size and/orweight. Moreover, the compact, inert energy sources of the invention canbe used to provide short duration electrical output. Since the materialsretained within the fuel cells are non-corrosive and typically nototherwise hazardous, it is practical to recharge the fuel cells withfuel, with the recharging done by the consumer or through a service suchas a mail order service.

[0007] Moreover, in certain aspects, the invention provides fuel cellsthat use active transport of protons to increase sustainable efficiency.Fuel cells of the invention can also be electrically recharged.

SUMMARY OF THE INVENTION

[0008] In one aspect, the invention provides a fuel cell comprising afirst compartment, a second compartment and a barrier separating thefirst and second compartments, wherein the barrier comprises a protontransporting moiety.

[0009] In another aspect, the invention provides a fuel cell a firstcompartment; a second compartment; a barrier separating the firstcompartment from the second compartment; a first electrode; a secondelectrode; a redox enzyme in the first compartment in communication withthe first electrode to receive electrons therefrom, the redox enzymeincorporated in a lipid composition; an electron carrier in the firstcompartment in chemical communication with the redox enzyme; and anelectron receiving composition in the second compartment in chemicalcommunication with the second electrode, wherein, in operation, anelectrical current flows along a conductive pathway formed between thefirst electrode and the second electrode.

BRIEF DESCRIPTION OF THE DRAWING

[0010]FIG. 1 displays a perspective view of the interior of a fuel cellwith three chambers.

[0011]FIG. 2 illustrates a fuel cell exhibiting certain preferredaspects of the present invention.

[0012]FIGS. 3A, 3B and 3C illustrate a similar fuel cell withscavenger-containing segment.

[0013]FIGS. 4A and 4B show a top view of a fuel cell with two chambers.

[0014]FIG. 5A shows a top view of a fuel cell with two chambers, whileFIG. 5B shows a side view.

[0015]FIG. 6 shows a fuel cell where the fluids bathing the twoelectrodes are segregated.

[0016]FIG. 7 shows a fuel cell with incorporated light regulation and asensor.

DEFINITIONS

[0017] The following terms shall have, for the purposes of thisapplication, the respective meaning set forth below.

[0018] electron carrier: An electron carrier is a composition thatprovides electrons in an enzymatic reaction. Electron carriers include,without limitation, reduced nicotinamide adenine dinucleotide (denotedNADH; oxidized form denoted NAD or NAD⁺), reduced nicotinamide adeninedinucleotide phosphate (denoted NADPH; oxidized form denoted NADP orNADP⁺), reduced nicotinamide mononucleotide (NMNH; oxidized form NMN),reduced flavin adenine dinucleotide (FADH₂; oxidized form FAD), reducedflavin mononucleotide FMNH₂; oxidized form FMN), reduced coenzyme A, andthe like.

[0019] Electron carriers include proteins with incorporatedelectron-donating prosthetic groups, such as coenzyme A, protoporphyrinIX, vitamin B12, and the like Further electron carriers include glucose(oxidized form: gluconic acid), alcohols (e.g., oxidized form:ethylaldehyde), and the like. Preferably the electron carrier is presentin a concentration of 1 M or more, more preferably 1.5 M or more, yetmore preferably 2 M or more.

[0020] electron-receiving composition: An electron-receiving compositionreceives the electrons conveyed to the cathode by the fuel cell.

[0021] electron transfer mediator: An electron transfer mediator is acomposition which facilitates transfer to an electrode of electronsreleased from an electron carrier.

[0022] redox enzyme: An redox enzyme is one that catalyzes the transferof electrons from an electron carrier to another composition, or fromanother composition to the oxidized form of an electron carrier.Examples of appropriate classes of redox enzymes include: oxidases,dehydrogenases, reductases and oxidoreductases. Additionally, otherenzymes, will redox catalysis as their secondary property could also beused e.g., superoxide dismutase.

[0023] composition. Composition refers to a molecule, compound, chargedspecies, salt, polymer, or other combination or mixture of chemicalentities.

DETAILED DESCRIPTION

[0024]FIG. 1 illustrates features of an exemplary battery such as a fuelcell 10. The fuel cell 10 has a first chamber 1 containing an electroncarrier, with the textured background fill of the first chamber 1illustrating that the solution can be retained within a porous matrix(including a membrane). Second chamber 2 similarly contains anelectrolyte (and can be the same material as found in the first chamber)in a space, which space can also be filled with a retaining matrix,intervening between porous first electrode 4 and porous second electrode5. A face of second electrode 5 contacts the space of third chamber 3,into which an electron receiving molecule, typically a gaseous moleculesuch as oxygen, is introduced. First electrical contact 6 and secondelectrical contact 7 allow a circuit to be formed between the twoelectrodes.

[0025] The optional porous retaining matrix can help retain solution in,for example, the second chamber 2 and minimize solution spillover intothe third chamber 3, thereby maintaining a surface area of contactbetween the electron receiving molecule and the second electrode 5. Insome embodiments, the aqueous liquid in the first chamber 1 and secondchamber 2 suspends non-dissolved reduced electron carrier, therebyincreasing the reservoir of reduced electron carrier available for useto supply electrons to the first electrode 4. In another example, wherethe chambers include a porous matrix, a saturated, solution can beintroduced, and the temperature reduced to precipitate reduced electroncarrier within the pores of the matrix. Following precipitation, thesolution phase can be replaced with another concentrated solution,thereby increasing the amount of electron carrier, which electroncarrier is in both solid and solvated form.

[0026] It will be recognized that the second chamber can be made up of apolymer electrolyte, such as one of those described above.

[0027] The reaction that occurs at the first electrode can beexemplified with NADH as follows:

H₂O+NADH z,900 NAD⁺+H₃O³⁰+2{overscore (e)}  (3)

[0028] Preferred enzymes relay the electrons to mediators that conveythe electrons to the anode electrode. Thus, if the enzyme normallyconveys the electrons to reduce a small molecule, this small molecule ispreferably bypassed. The corresponding reaction at the second electrodeis:

2H₃O⁺+½O₂+2z,900 3H₂O   (2)

[0029] Using reaction 2, preferably the bathing solution is buffered toaccount for the consumption of hydrogen ions, or hydrogen ion donatingcompounds must be supplied during operation of the fuel cell. Thisaccounting for hydrogen ion consumption helps maintain the pH at a valuethat allows a useful amount of redox enzymatic activity. To avoid thisissue, an alternate electron receiving molecule with an appropriateoxidation/reduction potential can be used. For instance, periodic acidcan be used as follows:

H₃O⁺+H₅IO₆+2{overscore (e)}z,900 IO ₃+4H₂O   (4)

[0030] The use of this reaction at the cathode results in a netproduction of water, which, if significant, can be dealt with, forexample, by providing for space for overflow liquid. Such alternativeelectron receiving molecules are often solids at operating temperaturesor solutes in a carrier liquid, in which case the third chamber 3 shouldbe adapted to carry such nongaseous material. Where, as with periodicacid, the electron receiving molecule can damage the enzyme catalyzingthe electron releasing reaction, the second chamber 2 can have asegment, as illustrated as item 8 in fuel cell 10′ of FIG. 2, containinga scavenger for such electron receiving molecule.

[0031] In a preferred embodiment, the electrodes comprise metallizationson each side of a non-conductive substrate. For example, in FIG. 3A themetallization on a first side of dielectric substrate 42 is the firstelectrode 44, while the metallization on the second side is the secondelectrode 45. Perforations 49 function as the conduit between the anodeand cathode of the fuel cell, as discussed further below. Theillustration of FIG. 3A, it will be recognized, is illustrative of therelative geometry of this embodiment. The thickness of dielectricsubstrate 42 is, for example, from 15 micrometer (μm) to 50 micrometer,or, from 15 micrometer to 30 micrometer. The width of the perforationsis, for example, from 20 micrometer to 80 micrometer. Preferably,perforations comprise in excess of 50% of the area of any area of thedielectric substrate involved in transport between the chambers, such asfrom 50 to 75% of the area. In certain preferred embodiments, thedielectric substrate is glass or an polymer, such as polyvinyl acetateor soda lime silicate.

[0032]FIG. 3B illustrates the electrodes framed on a perforatedsubstrate in more detail. The perforations 49 together with thedielectric substrate 42 provide a support for lipid bilayers (i.e.,membranes) spanning the perforations. Such lipid bilayers canincorporate at least a first enzyme or enzyme complex (hereafter “firstenzyme”) 62 effective (i) to oxidize the reduced form of an electroncarrier, and preferably (ii) to transport, in conjunction with theoxidation, protons from the fuel side 41 to the product side 43 of thefuel cell 50. Preferably, the first enzyme 62 is immobilized in thelipid bilayer with the appropriate orientation to allow access of thecatalytic site for the oxidative reaction to the fuel side andasymmetric pumping of protons. However, as the fuel is substantiallyisolated on the fuel side 41, an enzyme inserted into the lipid bilayerwith the opposite orientation is without an energy source.

[0033] Examples of particularly preferred enzymes providing one or bothof the oxidation/reduction and proton pumping functions include, forexample, NADH dehydrogenase (e.g., from E. coli. Tran et al.,“Requirement for the proton pumping NADH dehydrogenase I of Escherichiacoli in respiration of NADH to fumarate and its bioenergeticimplications,” Eur. J. Biochem. 244:155, 1997), NADPH transhydrogenase,proton ATPase, and cytochrome oxidase and its various forms. Methods ofisolating such an NADH dehydrogenase enzyme are described in detail, forexample, in Braun et al., Biochemistry 37:1861-1867, 1998; and Bergsmaet al., “Purification and characterization of NADH dehydrogenase fromBacillus subtilis,” Eur. J. Biochem. 128:151-157, 1982. The lipidbilayer can be formed across the perforations 49 and enzyme incorporatedtherein by, for example, the methods described in detail in Niki et al.,U.S. Pat. No. 4,541,908 (annealing cytochrome C to an electrode) andPersson et al., J. Electroanalytical Chem. 292:115, 1990. Such methodscan comprise the steps of: making an appropriate solution of lipid andenzyme, where the enzyme may be supplied to the mixture in a solutionstabilized with a detergent; and, once an appropriate solution of lipidand enzyme is made, the perforated dielectric substrate is dipped intothe solution to form the enzyme-containing lipid bilayers. Sonication ordetergent dilution may be required to facilitate enzyme incorporationinto the bilayer. See, for example, Singer, Biochemical Pharmacology31:527-534, 1982; Madden, “Current concepts in membrane proteinreconstitution,” Chem. Phys. Lipids 40:207-222, 1986; Montal et al.,“Functional reassembly of membrane proteins in planar lipid bilayers,”Quart. Rev. Biophys. 14:1-79, 1981; Helenius et al., “Asymmetric andsymmetric membrane reconstitution by detergent elimination,” Eur. J.Biochem. 116:27-31, 1981; Volumes on biomembranes (e.g., Fleischer andPacker (eds.)), in Methods in Enzymology series, Academic Press.

[0034] Using enzymes having both the oxidation/reduction and protonpumping functions, and which consume electron carrier, the acidificationof the fuel side caused by the consumption of electron carrier issubstantially offset by the export of protons. Net proton pumping inconjunction with reduction of an electron carrier can exceed 2 protonsper electron transfer (e.g., up to 3 to 4 protons per electrontransfer). Accordingly, in some embodiments care must be taken to bufferor accommodate excess de-acidification on the fuel side or excessacidification of the product side. Alternatively, the rate of transportis adjusted by incorporating a mix of redox enzymes, some portion ofwhich enzymes do not exhibit coordinate proton transport. In someembodiments, care is taken especially on the fuel side to moderateproton export to match proton production. Acidification orde-acidification on one side or another of the fuel cell can also bemoderated by selecting or mixing redox enzymes to provide a desiredamount of proton production. Of course, proton export from the fuel sideis to a certain degree self-limiting, such that in some embodiments thetheoretical concern for excess pumping to the product side is of, atbest, limited consequence. For example, mitochondrial matrix proteinswhich oxidize electron carriers and transport protons operate to createa substantial pH gradient across the inner mitochondrial membrane, andare designed to operate as pumping creates a relatively high pH such aspH 8 or higher. (In some embodiments, however, care is taken to keep thepH in a range closer to pH 7.4, where many electron carriers such asNADH are more stable.) Irrespective of how perfectly proton productionis matched to proton consumption, the proton pumping provided by thisembodiment of the invention helps diminish loses in the electrontransfer rate due to a shortfall of protons on the product side.

[0035] In some embodiments, proton pumping is provided by a light-drivenproton pump such as bacteriorhodopsin. Recombinant production ofbacteriorhodopsin is described, for example, in Nassal et al., J. Biol.Chem. 262:9264-70, 1987. All trans retinal is associated withbacteriorhodopsin to provide the light-absorbing chromophore. Light topower this type of proton pump can be provided by electronic lightsources, such as LEDs, incorporated into the fuel cell and powered by a(i) portion of energy produced from the fuel cell, or (ii) a translucentportion of the fuel cell casing that allows light from room lighting orsunlight to impinge the lipid bilayer. For example, illustrated in FIG.7 is a fuel cell 400 in which light control devices 71 are incorporated.These light control devices 71 contain, for example, LEDs or liquidcrystal shutters. Liquid crystal shutters have a relatively opaque and arelatively translucent state and can be electronically switched betweenthe two states. An eternal light source, such as the light provided byroom lighting or sunlight can be regulated through the use of liquidcrystal shutters or other shuttering device. In some embodiments, thelight control devices are individually regulated or regulated in groupsto aid in regulating the amount of light conveyed to the proton pumpprotein. Preferably, the light control devices 71 have lenses to directthe light to focus primarily at the dielectric substrate 42,particularly those portions containing lipid bilayers incorporating theproton, pumps. A monitoring device 72 can operate to monitor a conditionin the fuel cell, such as the pH or the concentration of electroncarrier, and relay information to a controller 73 which operates tomoderate an aspect of the operation of the fuel cell should monitoredvalues dictate such action. For example, the controller 73 can moderatethe level of light conveyed by the light control devices 71 dependingupon the pH of the fuel side 41. Note that in one embodiment an externallight source is allowed to energize the proton pump without the use ofany light-regulating devices.

[0036] In another embodiment, redox enzyme is deposited on or adjacentto the first electrode, while a proton transporter is incorporated intothe lipid bilayers of the perforations.

[0037] In another embodiment, a second enzyme 63 is incorporated intothe fuel cell, such as into the lipid bilayer or otherwise on the firstelectrode or in the first chamber, to facilitate proton transport orgeneration in the first chamber during recharge mode, thereby addingprotons to the fuel side. The second enzyme can be the same as, ordistinct from, the enzyme that transports protons during forwardoperation. An example of this second enzyme include transportingproteins with lower redox potential relative to, for example, NADsuccinate dehydrogenase in conjunction with the CoQH₂-cyt c reductasecomplex. Also useful are lactate dehydrogenase and malate dehydrogenase,both enzymes isolated from various sources available from Sigma ChemicalCo., St. Louis, Mo. For example, bacteriorhodopsin can also be used withan orientation appropriate for this use in the recharge mode.

[0038] In some embodiments, the recharge mode operates to regenerateNADH, but does not reverse pump protons.

[0039] The perforations 49 are illustrated as openings. However, thesecan also comprise porous segments of the dielectric substrate 42.Alternatively, these can comprise membranes spanning the perforations 49to support the lipid bilayer. Preferably, the perforations encompass asubstantial portion of the surface area of the dielectric substrate,such as 50%. Preferably, enzyme density in the lipid bilayer is high,such as 2×10¹²/mm².

[0040] The orientation of enzyme in the lipid bilayer can be random,with effectiveness of proton pumping dictated by the asymmetric presenceof substrate such as protons and electron carrier. Alternatively,orientation is established for example by using antibodies to the enzymepresent on one side of the membrane during formation of the enzyme-lipidbilayer complex.

[0041] The perforations 49 and metallized surfaces (first electrode 44and second electrode 45) of the dielectric substrate 42 can beconstructed, for example, with masking and etching techniques ofphotolithography well known in the art. Alternatively, the metallizedsurfaces (electrodes can be formed for example by (1) thin filmdeposition through a mask, (2) applying a blanket coat of metallizationby thin film then photo-defining, selectively etching a pattern into themetallization, or (3) Photo-defining the metallization pattern directlywithout etching using a metal impregnated resist (DuPont Fodel process,see, Drozdyk et. al. “Photopatternable Conductor tapes for PDPapplications” Society for Information Display 1999 Digest, 1044-1047;Nebe et al., U.S. Pat. No. 5,049,480). In one embodiment, the dielectricsubstrate is a film. For example, the dielectric can be a porous filmthat is rendered non-permeable outside the “perforations” by themetallizations. The surfaces of the metal layers can be modified withother metals, for instance by electroplating. Such electroplatings canbe, for example, with chromium, gold, silver, platinum, palladium,nickel, mixtures thereof, or the like, preferably gold and platinum. Inaddition to metallized surfaces, the electrodes can be formed by otherappropriate conductive materials, which materials can be surfacemodified. For example, the electrodes can be formed of carbon(graphite), which can be applied to the dielectric substrate by electronbeam evaporation, chemical vapor deposition or pyrolysis. Preferably,surfaces to be metallized are solvent cleaned and oxygen plasma ashed.

[0042] As illustrated in FIG. 3C, electrical contact 54 connects thefirst electrode 44 to a prospective electrical circuit, while electricalcontact 55 connects the second electrode 45.

[0043] In one embodiment, the product side of the fuel cell is comprisedof an aqueous liquid with dissolved oxygen. In an embodiment, at least aportion of the wall retaining such aqueous liquid is oxygen permeable,but sufficiently resists transmission of water vapor to allow a usefulproduct lifetime with the aqueous liquid retained in the fuel cell. Anexample of an appropriate polymeric wall material is an oxygen permeableplastic. In contrast, the fuel side is preferably constructed ofmaterial that resists the incursion of oxygen. The fuel cell can be madeanaerobic by flushing to purge oxygen with an inert gas such as nitrogenor helium. In some rechargeable embodiments, the electron-receivingcomposition is regenerated during recharging mode, thereby eliminatingor reducing the need for an outside supply of such electron-receivingcomposition.

[0044] The fuel cell of the invention can preferably be recharged byapplying an appropriate voltage to inject electrons into the fuel sideto allow the first enzyme to catalyze the reverse reaction. Inparticularly preferred embodiments, the first enzyme has both theoxidation/reduction and proton pumping functions and operates to reversepump protons from the product side to the fuel side during recharging.Thus, the reverse pumping supplies the protons consumed in generating,for example, NADH from (i) NAD⁺ and (ii) the injected electrons andprotons. Note that in reverse operation the injected electrons act firstto reduce any oxygen resident in the fuel side, as this reaction isenergetically favored. Once any such oxygen is consumed, the electronscan contribute to regenerating the reduced electron carrier.

[0045] The above discussion of the embodiments using proton transportfocus on the use of both faces of a substrate to provide the electrodes,thereby facilitating a more immediate transfer of protons to the productside where the protons are consumed in reducing the electron-receivingcomposition. However, it will be recognized that in this embodimentstructures such as a porous matrix can be interposed between the fuelside and the product side. Such an intervening structure can operate toprovide temperature shielding or scavenger molecules that protect, forexample, the enzymes from reactive compounds.

[0046] The fuel cell operates within a temperature range appropriate forthe operation of the redox enzyme. This temperature range typicallyvaries with the stability of the enzyme, and the source of the enzyme.To increase the appropriate temperature range, one can select theappropriate redox enzyme from a thermophilic organism, such as amicroorganism isolated from a volcanic vent or hot spring. Nonetheless,preferred temperatures of operation of at least the first electrode areabout 80° C. or less, preferably 60° C. or less, more preferably 40° C.or 30° C. or less. The porous matrix is, for example, made up of inertfibers such as asbestos, sintered materials such as sintered glass orbeads of inert material.

[0047] The first electrode (anode) can be coated with an electrontransfer mediator such as an organometallic compound which functions asa substitute electron recipient for the biological substrate of theredox enzyme. Similarly, the lipid bilayer of the embodiment of FIG. 3or structures adjacent to the bilayer can incorporate such electrontransfer mediators. Such organometallic compounds can include, withoutlimitation, dicyclopentadienyliron (C₁₀H₁₀Fe, ferrocene), availablealong with analogs that can be substituted, from Aldrich, Milwaukee,Wis., platinum on carbon, and palladium on carbon. Further examplesinclude ferredoxin molecules of appropriate oxidation/reductionpotential, such as the ferredoxin formed of rubredoxin and otherferredoxins available from Sigma Chemical . Other electron transfermediators include organic compounds such as quinone and relatedcompounds. The electron transfer mediator can be applied, for example,by screening or masked dip coating or sublimation. The first electrodecan be impregnated with the redox enzyme, which can be applied before orafter the electron transfer mediator. One way to assure the associationof the redox enzyme with the electrode is simply to incubate a solutionof the redox enzyme with electrode for sufficient time to allowassociations between the electrode and the enzyme, such as Van der Waalsassociations, to mature. Alternatively, a first binding moiety, such asbiotin or its binding complement avidin/streptavidin, can be attached tothe electrode and the enzyme bound to the first binding moiety throughan attached molecule of the binding complement.

[0048] The redox enzyme can comprise any number of enzymes that use anelectron carrier as a substrate, irrespective of whether the primarybiologically relevant direction of reaction is for the consumption orproduction of such reduced electron carrier, since such reactions can beconducted in the reverse direction. Examples of redox enzymes furtherinclude, without limitation, glucose oxidase (using NADH, available fromseveral sources, including number of types of this enzyme available fromSigma Chemical), glucose-6-phosphate dehydrogenase (NADPH, BoehringerMannheim, Indianapolis, Ind.), 6-phosphogluconate dehydrogenase (NADPH,Boehringer Mannheim), malate dehydrogenase (NADH, Boehringer Mannheim),glyceraldehyde-3-phosphate dehydrogenase (NADH, Sigma, BoehringerMannheim), isocitrate dehydrogenase (NADH, Boehringer Mannheim; NADPH,Sigma), and α-ketoglutarate dehydrogenase complex (NADH, Sigma).

[0049] The redox enzyme can also be a transmembrane pump, such as aproton pump, that operates using an electron carrier as the energysource. In this case, enzyme can be associated with the electrode in thepresence of detergent and/or lipid carrier molecules which stabilize theactive conformation of the enzyme. As in other embodiments, an electrontransfer mediator can be used to increase the efficiency of electrontransfer to the electrode.

[0050] Associated electron carriers are readily available fromcommercial suppliers such as Sigma and Boehringer Mannheim. Theconcentrations at which the reduced form of such electron carriers canbe as high as possible without disrupting the function of the redoxenzyme. The salt and buffer conditions are designed based on, as astarting point, the ample available knowledge of appropriate conditionsfor the redox enzyme. Such enzyme conditions are typically available,for example, from suppliers of such enzymes.

[0051] As illustrated for the fuel cell 100 in FIG. 4A (top view), asource reservoir 111 can be provided to supply reduced electron carriervia conduit 113, check-valve 112 and diffuser 114 to second chamber 102.Note that fuel cell 100 lacks a first chamber as this chamber oftenserves as a reservoir, which in fuel cell 100 is provided by sourcereservoir 111. Diffuser 115, conduit 116, and pump 117 provide thepathway and motive power for conveying spent liquid containing theelectron carrier (often merely having reduced effectiveness in poweringthe fuel cell) to an output reservoir 118. Fuel cell 100 further has afirst electrode 104, second electrode 105, third chamber 103, air pump121, air inlet 122, and air outlet 123. The various pumps can beoperated off of a battery, which can be recharged and regulated usingenergy from the fuel cell, or can come into operation after the fuelcell begins generating current. As illustrated in FIG. 4B, voltage orcurrent monitor M can monitor the performance the fuel cell in providingvoltage to the circuit comprising resister(s) R. Monitor M can relayinformation to the controller, which uses the information to regulateoperation of one or more of the pumps.

[0052]FIG. 5A illustrates a fuel cell 200 (top view) in which anacid/base reservoir 231 serves to supply a source of a material requiredto account for any material imbalances in the reaction equations at thefirst and second electrodes. The acid/base reservoir 231 is connectedvia conduit 232, first actuated valve 233, and diffuser 234 to a secondchamber 202. Liquid from source reservoir 211 is delivered via checkvalve 212A and second actuated valve 212B. In one example of operation,second actuated valve 212B is normally open, and first actuated valve233 is normally closed. These valve positions are reversed when thecontroller detects the need for fluid from acid/base reservoir 231(e.g., because of a signal received from a pH monitor) and operates pump117 (e.g., by use of a stepper motor) to draw fluid into the secondchamber 202.

[0053] It will be recognized that the pump and valve arrangements inFIGS. 4A through 5B are for illustration only, as numerous alternativearrangements will be recognized by those of ordinary skill. The plumbingof the fuel cell can be arranged to maintain a chamber less thanatmospheric pressure, for instance to help reduce fluid leakage throughvarious porous materials. The pores in various porous materials can beselected to allow such diffusion as is needed while minimizing fluidflow across the porous materials, such as bulk liquid flow into achamber designed to bring gas into contact with a porous electrode.

[0054] The chambers of fluid which the first and second electrodescontact can be independent, as illustrated in FIG. 6. In fuel cell 300,the solution bathing the first electrode (anode) is fed through conduit313A, while that bathing the second electrode (cathode) is suppliedthrough conduit 313B. Flow is illustrated as regulated by pumps 317A and317B. In the illustrated fuel cell, the bathing solutions arereplenished as needed to account for the necessary imbalance in thechemistries occurring in the segregated cells.

[0055] Cells can be stacked, and electrodes arranged in a number of waysto increase the areas of contact between electrodes and reactants. Thesestacking and arranging geometries can be based on well-known geometriesused with conventional fuel cells.

[0056] It will be recognized that where the electron carrier has anappropriate electrochemical potential relative to the electron-receivingmolecule, the cell can be operated so that the oxidized form of theelectron carrier receives the electrons through an enzyme catalyzedevent. For example, the electron carrier and the electron-receivingmolecule can both be of the class exemplified for electron carriers, butwith distinct electrochemical potentials. Thus, both the fuel side andproduct side reactions can be enzyme catalyzed. In fact, even with suchtraditional electron-receiving composition as oxygen, the product sidereaction can be enzyme catalyzed.

[0057] In one embodiment of the invention, the fuel cell does notincorporate a proton pump. Preferably, in this embodiment the redoxenzyme is associated with a lipid component, such as a compositioncontaining phospholipid, steroids (such as sterols), glycolipids,sphinoglipids, triglyceride or other components typically incorporatedinto intracellular or external cellular membranes, while still beingsufficiently associated with the electrodes to convey electrons. Theenzyme is preferably incorporated into a lipid bilayer. The barrier canbe separating component such as is used in a typical fuel cell, whichpreferably conveys protons between the first and second chambers, thoughwithout requiring proton pumping.

[0058] The following examples further illustrate the present invention,but of course, should not be construed as in any way limiting its scope.

EXAMPLE

[0059] The test apparatus consisted of a 5 ml reaction vessel which heldthe fuel and into which copper or other electrodes were dipped. Theelectrodes were in turn connected to a high impedance voltmeter for opencircuit voltage measurements or to a low impedance ammeter for shortcircuit current measurements. Various test configurations were employedto establish a baseline with which to measure performance of the cell.Testing was done by dipping electrodes in the fuel solution andmeasuring current and/or voltage as a function of time.

[0060] The reaction which drove the cell was the oxidation ofnicotinamide-adenine dinucleotide hydride (NADH) which is catalyzed bythe enzyme glucose oxidase (GOD) in the presence of glucose. Thisreaction yielded NAD⁺, a proton (H⁺) and 2 free electrons.

H₂O+NADH=NAD⁺+H₃O⁺+2{overscore (e)}

[0061] The reaction toke place at one electrode, which was a metallizedplastic strip coated with the enzyme GOD. This half-reaction was coupledthrough an external circuit to the formation of water or hydrogenperoxide from protons, dissolved oxygen, and free electrons at the otherelectrode.

[0062] Fuels used were solutions of glucose, NADH or combinationsthereof, distilled deionized water or a 50 mM solution of Tris™ 7.4buffer. (NADH is most stable in a pH 7.4 environment.) Electrodematerials were copper (as a reference) and metallized plastic stripscoated with GOD (a commercially available product).

[0063] Test configurations employed as well as initial results were asfollows:

[0064] Configuration 1

[0065] Electrode 1: Copper

[0066] Electrode 2: Copper

[0067] Solution: 50 mM tris 7.4 buffer

[0068] Voltage: −7.5 mV

[0069] Current: 3 μA initially decaying to −2.2 μA within 3 minutes,fairly constant thereafter.

[0070] Configuration 2

[0071] Electrode 1: Copper

[0072] Electrode 1: GOD coated strip

[0073] Solution: 50 mM tris 7.4 buffer

[0074] Voltage: +350 mV

[0075] Current: >20μA (+) initially decaying to +4 μA within 2 minutes,fairly constant thereafter.

[0076] Configuration 3

[0077] Electrode 1: Copper

[0078] Electrode 2: Copper

[0079] Solution: 10 mM glucose in 50 mM tris 7.4 buffer

[0080] Voltage: −6.3 mVCurrent: −1.7 μA, fairly constant after initialdropoff.

[0081] Configuration 4

[0082] Electrode 1: Copper

[0083] Electrode 2: GOD coated strip

[0084] Solution: 10 mM glucose in 50 mM tris 7.4 buffer

[0085] Voltage: +350 mV

[0086] Current: >20 μA (+) initially decaying to˜+2 μA within 2 minutes,fairly constant thereafter.

[0087] Configuration 5

[0088] Electrode 1: Copper

[0089] Electrode 2: Copper

[0090] Solution: 10 mM glucose +10 mM NADH in 50 mM tris 7.4 buffer

[0091] Voltage: −290 mV slowly increasing to—320 after 4 minutes

[0092] Current: −25 μA, decaying to −21 μA after 2 minutes.

[0093] Configuration 6

[0094] Electrode 1: Copper

[0095] Electrode 2: GOD coated strip

[0096] Solution: 10 mM glucose +10 mM NADH in 50 mM tris 7.4 buffer

[0097] Voltage: +500 mV decaying to +380 after 2 minutes

[0098] Current: >+30 μA, dropping rapidly to˜+1 μA after 1 minute.

[0099] All publications and references, including but not limited topatents and patent applications, cited in this specification are hereinincorporated by reference in their entirety as if each individualpublication or reference were specifically and individually indicated tobe incorporated by reference herein as being fully set forth. Any patentapplication to which this application claims priority is alsoincorporated by reference herein in its entirety in the manner describedabove for publications and references.

[0100] While this invention has been described with an emphasis uponpreferred embodiments, it will be obvious to those of ordinary skill inthe art that variations in the preferred devices and methods may be usedand that it is intended that the invention may be practiced otherwisethan as specifically described herein. Accordingly, this inventionincludes all modifications encompassed within the spirit and scope ofthe invention as defined by the claims that follow.

What is claimed:
 1. A battery comprising a first compartment, a secondcompartment and a barrier separating the first and second compartments,wherein the barrier comprises a proton transporting moiety.
 2. A batterycomprising: a first compartment; a second compartment; a barrierseparating the first compartment from the second compartment; saidbarrier having a proton transporting moiety; a first electrode; a secondelectrode; a redox enzyme in the first compartment in communication withthe first electrode to receive electrons therefrom; an electron carrierin the first compartment in chemical communication with the redoxenzyme; and an electron receiving composition in the second compartmentin chemical communication with the second electrode, wherein, inoperation, an electrical current flows along a conductive pathway formedbetween the first electrode and the second electrode.
 3. The battery ofclaim 2, wherein the first electrode is further associated with anelectron transfer mediator that transfers electrons from the redoxenzyme to the first electrode.
 4. The battery of claim 2, wherein theproton transporting protein comprises at least a portion of the redoxenzyme.
 5. The battery of claim 2, adapted to operate at the firstelectrode at a temperature of about 60° C. or less.
 6. The battery ofclaim 2, further comprising a reservoir for supplying to the vicinity ofat least one of the electrodes a component consumed in the operation ofthe battery and a pump for drawing such component to that vicinity. 7.The battery of claim 6, further comprising a controller which receivesdata on the operation of the battery and controls the pump in responseto the data.
 8. The battery of claim 2, wherein a light-driven protonpump protein comprises at least a portion of the proton transportingprotein, and further comprising: a source of light for powering thelight-driven proton pump protein.
 9. The battery of claim 2, furtherincorporating in the barrier a second protein, distinct from the first,adapted to facilitate reverse proton pumping when the battery isoperated in recharge mode.
 10. A method of operating a battery with afirst compartment and a second compartment comprising: enzymaticallyoxidizing an electron carrier and delivering the electrons to a firstelectrode in chemical communication with the first compartment;catalyzing the transfer of protons from the first compartment to thesecond compartment; and reducing an electron receiving molecule withelectrodes conveyed through a circuit from the first electrode to asecond electrode located in the second compartment.
 11. The method ofclaim 10, wherein the catalytic transfer of protons occurs inconjunction with the enzymatic oxidation of the electron carrier. 12.The method of claim 10, wherein at least a portion of the transfer ofprotons is driven by a light-driven proton pump protein, and the methodfurther comprises: directing light to the light-driven proton pump. 13.The method of claim 12, further comprising monitoring the pH of thefirst compartment and controlling the amount of light directed to thelight-driven proton pump such that relatively more light is directed atlower pH values.
 14. The method of claim 10, further comprising:applying a voltage to the electrodes of a polarity opposite thatgenerated by the normal operation of the battery to recharge thebattery.
 15. The method of claim 14, further comprising: enzymaticallytransporting protons from the second chamber to the first chamber inconnection with the applying the recharge voltage.
 16. The method ofclaim 15, wherein at least a portion of the enzymatic transport inrecharge mode is accomplished by an enzyme distinct from an enzymecatalyzing the majority of proton transport in a power producing mode.17. A battery comprising: a first compartment; a second compartment; abarrier separating the first compartment from the second compartment; afirst electrode; a second electrode; a redox enzyme in the firstcompartment in communication with the first electrode to receiveelectrons therefrom, the redox enzyme incorporated in a lipidcomposition; an electron carrier in the first compartment in chemicalcommunication with the redox enzyme; and an electron receivingcomposition in the second compartment in chemical communication with thesecond electrode, wherein, in operation, an electrical current flowsalong a conductive pathway formed between the first electrode and thesecond electrode.
 18. A method of operating a battery with a firstcompartment and a second compartment comprising: enzymaticallyoxidizing, with an enzyme incorporated into a lipid composition, anelectron carrier and delivering the electrons to a first electrode inchemical communication with the first compartment; and reducing anelectron receiving molecule with electrodes conveyed through a circuitfrom the first electrode to a second electrode located in the secondcompartment.